The present invention relates to the manufacture of cellular foam products, and to an improved method which yields an improved and more economical final product by controlling and maintaining proper foam formation conditions and reducing foam flash during the manufacture of such products.
As is well known, the manufacture of cellular foam products involves reaction processes which include gas generation during the transformation of the reaction constituents via polymerization from a liquid to a cream to foam to a gell state. An example of such a process is the manufacture of urethane foam products by way of water blown foam systems. Such systems involve the reaction of water and isocyanate, which reaction results in the creation of carbon dioxide gas which acts as a blowing agent. A fluorocarbon auxiliary blowing agent is often the urethane foam. Gas evolution control during the reaction process is attained by balancing gellation catalysts with blowing catalysts. One of the problems associated with producing urethane foam products is the control of gas release during the foaming and/or foam curing process. More particularly, as the urethane polymerization reaction progresses toward a gell state, the polymer is prone to voiding or collapsing if internal foam cell pressure is not maintained.
A related problem in the manufacture of cellular foam products arises when there are open areas in substructural inserts or substrates utilized in final foamed assemblies, such as with automotive instrument panel or door panel applications. Such open areas result in foam leakage referred to in the industry as "flash". The loss of gas pressure through excessive foam flash or inadequate mold sealing can result in pressure voiding, leading to the need for repairing or scrapping of the resulting foam assembly. Moreover, the creation of flash during the manufacturing process requires additional material and labor costs necessitated by the creation and removal of such flash. In current practice, many methods have been utilized to decrease gas leakage and to reduce the creation of flash, including taping holes in assembly substrates, utilizing plugs of various compositions, and building shut-offs in foam curing tools. However, such methods present disadvantages in that they involve additional tooling costs, labor costs, or do not yield consistent results. It is, therefore, desirable to provide a method for manufacturing cellular foam products which allows for more consistent control of gas pressure during polymerization reaction processes, so that the opportunity for internal cell voiding or collapse in such products is reduced. It is moreover desirable to provide such a method which provides for more consistent control of and reduction of foam leakage, so that the creation of flash in final foam product assemblies is minimized. It is further desirable to provide such a method which yields an attendant reduction in tooling costs, as well as the material and labor costs associated with repairing, scrapping and trimming operations in the manufacture of such foam products, so that the above objectives can be achieved more readily and economically than with present cellular foam product manufacturing techniques.
The present invention is intended to satisfy the above desirable features and objectives through the provision of a new and improved method of making cellular foam products, wherein the substructural insert or load supporting member of the product is preworked prior to the foaming process to yield an insert/adhesive/plastic film composite substrate which significantly reduces the problems of gas pressure loss and foam leakage during foaming and curing processes. More particularly, the insert is first pretreated with a spray adhesive on its foam supporting faces. A thin flexible plastic film is thereafter stretched and formed over the insert to allow for an intimate contact between the film and the adhesive coated foam supporting faces of the insert. This process is accomplished most readily by way of a vacuum forming operation which causes the film to vacuum form to the shape of the insert and provide a continuous film barrier along its foam supporting faces. The vacuum can be held for desired periods of time to enhance intimate contact between the plastic film, insert and adhesive to enable sufficient bonding therebetween. The vacuum is thereafter removed and the operator may trim the film as desired to prepare the resulting composite substrate for loading into a conventional foam cure mold for foaming. The invention results in a significant reduction in gas pressure leakage and foam flash, and the resulting composite substrate yields an improved and more economical final foam product. Due to the fact that foam is inhibited from flashing through the substrate by way of the continuous plastic film barrier, the invention also results in lower scrappage and increased productivity.
The above and other features of the invention will become apparent from a reading of the detailed description of the preferred embodiment, which makes reference to the following set of drawings.